The long-term goal of this project is to determine the role of tissue acid-base and metabolic derangements in the temporal and spatial progression of focal stroke. Focal models of ischemia are generally more relevant to human stroke process than are global models, since most human strokes involve the occlusion of a single process than are global models, since most human strokes involve the occlusion of a single vessel. However, a number of problems arise in focal stroke that have limited its usefulness as an experimental model: 1) the spatial configuration of the stroke is not reproducible and the affected regions vary between animals, and 2) the insult elicited by the occlusion is not restricted to the infarct but extends to adjacent regions which, unlike the ischemic focus, are partially perfused. The fate of these partially perfused peri-focal areas, their location, and their response to the insult will determine the eventual scope of infarcted tissue, and, therefore, the severity of the stroke. The necessary first step is to locate and define the condition of these compartments. This has been achieved by the intravenous injection of the diffusible dye, neutral red. The advantages of the neutral red technique are: 1) it visually defines infrazones of stroke, 2) it is compatible with metabolic microanalysis of the tissue, and 3) it is simple and inexpensive compared to other methods for indicating tissue perfusion. The distribution of neutral red delineates three major visible regions without ambiguity. The relationship between stain intensity and tissue perfusion will be evaluated in conjunction with iodoantipyrine metabolic and histological studies. The viability of the various regions will be assessed by evaluating certain metabolic and pH parameters at various stages of recovery in rat brain frozen in situ, sectioned on a cryostat, lyophilized and dissected in reference to the neutral red staining pattern. Energy balance in the areas of altered perfusion will be determined by the microquantitative measurement of ATP, P- creatine, glucose, glycogen, and lactate; and functional integrity assessed from the levels of GABA, glutamate, and cyclic nucleotides. The affected region will also be labeled with neutral red to determine the intracellular pH by spectral analysis, and for in vivo studies on potassium and hydrogen ion concentration using ion-selective extracellular microelectrodes. This use of neutral red permits, for the first time, a multidisciplinary approach to identify the spatial and temporal concomitants of focal stroke. This information collectively will serve as a basis for developing and evaluating new therapeutic regimens.